Sexual Nuclei in Lilium Mart agon . 467 
stage, and become differentiated in pairs in the usual way 
(Fig- 37)- 
Between the end of the second karyokinesis and the be- 
ginning of the third, some time elapses (vid. Table I), during 
which the embryo-sac increases in length. Vacuoles are 
formed which divide the pairs of nuclei from each other. The 
two micropylar nuclei continue egg-shaped and small : the 
lower ones are larger and of less regular shape. Very often 
the upper chalazal nucleus is flattened as if pressed between 
the lower one and a vacuole, while the lower chalazal nucleus 
is of a shape determined by that of the end of the embryo-sac 
into which it fits (Fig. 37). I have described elsewhere the 
curious difference apparent between the lower chalazal nucleus 
and the other three nuclei during the third karyokinesis in 
the embryo-sac h It is conspicuous as soon as the nuclear 
division begins. While the spirem ribbon in the three upper 
nuclei is beautifully differentiated, the lowest nucleus, though 
swollen, is still in the resting condition (Fig. 38). It then 
proceeds to divide by the direct or amitotic method (Figs. 
39-41). The chromatin aggregates at either end as the 
nucleus lengthens, and the linin network between the masses 
of chromatin is drawn out in threads. In the later stages 
of division these give the figure a strong resemblance to a 
badly preserved dispirem (Fig. 41). The nucleolus disappears 
during the process : sometimes a washy mass of semifluid 
nucleolar matter can be seen outside the nucleus (; n , Fig. 39). 
Meanwhile the karyokinetic division of the three upper 
nuclei goes on quite typically. We are chiefly concerned with 
the lower micropylar nucleus which will give rise by its 
division to the ovum and to the upper polar nucleus. The 
chromosomes however divide and their segments separate in 
exactly the same manner in all three figures. The process is 
also simultaneous, so that if one section of a series shows 
a single spindle in a particular stage, we are certain to find 
two others in neighbouring sections at exactly the same point 
1 E. Sargant, on direct Nuclear Division in the Embryo Sac of Lilium 
Martagon — Ann. of Bot, x. 1896. p. 107. 
